The present invention relates to an image processing device, and in particular, to an image processing device in which image information of the subject is inputted according to movement of the device along the surface the subject.
Description of the Related Art
These days, hand-held image scanners are widely used for inputting image information on subjects such as text on books etc. When such a hand-held image scanner is used for inputting image information, the scanner is placed on the subject and is needed to be moved manually in vertical scanning direction with respect to the subject such as a document. However, if the speed of the manual movement is too fast, image processing speed of the hand-held image scanner can not follow the input speed of the image information, and thus problems such as image contraction occurs.
In order to prevent such problems, some hand-held image scanners are designed to display the movement speed and let the operator recognize overspeed, or some hand-held image scanners are designed to make a warning beep when the movement speed is higher than a threshold speed, thereby operators can control the manual movement speed adequately.
However, with such conventional hand-held image scanners, the operator himself/herself has to judge the movement speed by seeing the display or by hearing the warning beep and control the movement speed. Here, response time needed for an operator to reduce the movement speed after hearing the warning beep etc. varies among individuals, and thus some operators may continue moving the hand-held image scanner at a movement speed higher than readable movement speed for a while, causing the image contraction, etc.
Meanwhile, in some image reading devices, the amount of image information to be processed by the device is reduced by curtailing or thinning out the amount of image information transferred therein, thereby the maximum image information input speed is raised, and problems such as image contraction are avoided. Such image reading devices are disclosed in Japanese Patent Application Laid-Open No.HEI6-291936 and in Japanese Patent Application Laid-Open No.HEI5-114996, for example.
FIG. 1 is a timing chart showing the `curtailing` operation of an image reading device which is disclosed in Japanese Patent Application Laid-Open No.HEI5-114996. In FIG. 1, `HSYNC` is a synchronous signal for a CCD image sensor. The period of the synchronous signal HSYNC is set at 4 ms, for example. The `CCDOUT` is output from the CCD image sensor whose resolution in horizontal scanning direction is 300 DPI (Dots Per Inch). In this case, the width of one pixel on the subject is approximately 84.7 .mu.m (2.54 cm/300), and pixel numbers (1, 2, 3, 4, 5) are shown in FIG. 1. `PMCK` is a clock signal for driving a stepping motor. Here, 4 pulses of the clock signal PMCK is included in the aforementioned 4 ms, therefore the stepping motor is driven at a clock frequency of 1000 PPS (Pulse Per Second). The clock frequency 1000 PPS corresponds to the aforementioned resolution 300 DPI, since 4 pulses of the clock signal PMCK correspond to one pixel.
When `curtailing` is not executed, image information of every pixel on the subject (1, 2, 3, 4, . . . ) is read by the image reading device. In this case, the intensity of white of each pixel detected by the CCD image sensor is quantized by a 6-bit A/D converter and the quantized 6-bit value (0-65 in decimal digits) of every pixel is transferred to an external device such as a personal computer via an interface circuit of the image reading device.
When `curtailing` is executed in the curtailing mode #1 in FIG. 1, image information of every other pixel on the subject (1, 3, 5, . . . ) is read by the image reading device. In this case, the intensity of white of every other pixel detected by the CCD image sensor is quantized by the same 6-bit A/D converter and the quantized 6-bit value of every other pixel is transferred to the external device via the interface circuit.
When `curtailing` is executed in the curtailing mode #2 in FIG. 1, image information of each pixel whose pixel number is a multiple of 4 (4, 8, . . . ) is read by the image reading device. In this case, the intensity of white of each pixel whose pixel number is a multiple of 4 is quantized by the same 6-bit A/D converter and the quantized 6-bit values of the pixels are transferred to the external device via the interface circuit.
However, with such curtailing or thinning out of the transferred image information (i.e. pixel skipping), image information of some pixels has to disappear completely, and thus the quality of the image is necessarily deteriorated.
Further, in the case of color image reading, a sequence of three pixels is used for acquiring the intensity of three primary colors (Red, Green, Blue), that is, a pixel for acquiring the intensity of red, a pixel for acquiring the intensity of green, and a pixel for acquiring the intensity of blue are arranged in a row, and the sequence of three pixels for acquiring the intensity of RGB primary colors is repeated along each line in the horizontal scanning direction. In such a case, the curtailing (pixel skipping) method is disadvantageous, since inconsistencies in color (wrong colors) occur due to the pixel skipping.